The field of frameless stereotaxy is now a very active one. In the early works of Watanabe (1986) and Kosugi (1987), and other workers such as Guthrie and Adler in the same time frame, a digitized space pointer or stereotactic navigator was used which involved an encoded mechanical arm. This navigating arm was placed near the patient during surgery. Typically, reference points such as radiopaque skin markers or tattoos where radiopaque skin markers could be placed were located on the patient's skin. The skin markers were in place at the time the patient is scanned by an image scanner prior to surgery, and they appeared as reference marker images on the image scan data from for example a tomographic scan. The scan could be from CT, MRI, PET, or other modality, and appropriate markers visible on these scans could be used. One of the objectives was to transform from the image scan coordinate system to a reference frame associated with the stereotactic navigator, and in the case of Watanabe, Kosugi, Guthrie, and Adler, this was the reference frame of a digitized mechanical arm. Other types of reference frames and associated digitizers have been developed involving ultrasonic, optical, and magnetic coupling between a probe whose position is to be determined or tracked in space relative to the patient and a detector or sender system which represents the reference system for the space digitizer located near the patient's head. At the time of surgery, such a probe, whose position can be determined in the digitizer coordinate system, (herein referred to as the stereotactic coordinate system) could be used to touch each of the reference markers in sequence, thereby determining their positions relative to the stereotactic coordinate system of the digitizer. At this point, since the positions of the reference points are known with respect to their reference point images in the image scan coordinate system, and the physical reference points positions are known with respect to the coordinate system of the digitizer or the reference (stereotactic) coordinate system in space, then a mapping, transformation, or correspondence can be made between these two coordinate systems. Thereafter, the position of the surgical instrument which is being tracked by the digitizer system can be represented in the coordinate space of the image scan data. Thus, as the pointer or surgical instrument is moved in space near the patient's anatomy, a representation of where it will be relative to the inside of the patient's head, as represented by the image scan data, can be determined. All of this data: the image scan data, reference marker images, digitizing data from the reference frame of the digitizer, positions of the physical reference markers, can be loaded into a computer or computer graphic workstation and the transformations can be made by matrix transformations within the workstation, as explained in Kosugi's paper. Thereafter the position of the space probe can be represented in the image scan data as a representation of the slice containing the tip of the probe, or slice containing the probe itself (as in an oblique slice) or representation of the probe within the 3-D slices, or 3-D rendering of the image scan data itself.
It would be convenient to be able to put the reference markers on the patient's body or head in a repeatable way and in a simple way for an operator. It would also be convenient to have a structure which can retain the reference markers so that they can be returned onto the patient's body repeatedly, as for example in the scan episode and in the surgical episode, so easy referencing of multiple markers can be done. It is also convenient if dynamic reference markers could be installed or coupled on the patient's body in a common structure with the reference markers, or convenient if the dynamic markers are the reference markers themselves which can be tracked by the space digitizer or its detection system in the coordinate reference frame of the space digitizer, so that the patient's movement can be tracked dynamically, and thereby corrections in the transformation between the image scan data coordinate system and the stereotactic coordinate system can be made. It would furthermore be convenient if the attachment means for the reference markers and the dynamic reference markers could also alternatively couple to a graphics reference means which can index all of the scan slices in a unified image scan coordinate system to eliminate errors due to patient's movement during the scanning or to correct for aberrations in the scan slice sequence itself.
Thus, it is an objective of the present invention to provide an apparatus, a means, and associated technique, which can easily attach to and which may be repeatedly re-attached to the patient's anatomy if desired, in essentially the same location which contains a plurality or pattern of reference markers to be used for frameless stereotaxy.
It is also an objective of the present invention that the patient attachment means can be placed on or connected to the patient's skin easily and that it can be quickly placed and re-placed at the time of scanning with minimal effort or technical knowledge.
It is also an object of the present invention that the patient attachment device can include dynamic reference markers which can be detected rapidly by the space digitizer or the space digitizer detection or transmission means so that rapid corrections of patient movement, either in the scanner or in the operative setting, can be made so as to correct the transformation between the image scan coordinate system and the stereotactic coordinate system of the space digitizer.
It is an objective of the present invention to provide a system which is non-invasive and would not necessarily require breaking of the patient's skin or any discomfort for the patient to have the patient attachment device installed on the patient.
It is also an object of the present invention to provide a patient attachment device which can be cooperatively coupled to a graphic reference means with diagonal and parallel elements such that the image scan slice data or tomographic scan data can be indexed relative to the patient attachment device, and therefore to the patient's body, in a consistent image coordinate system.